This invention relates to improvements in a semiconductor device, and more particularly to a high power semiconductor device including means for preventing a secondary accident from occuring due to failure of the device.
Semiconductor devices such as semiconductor rectifier diodes, thyristors, etc., gradually increase in capacity, and there have been proposed a variety of circuits employing such high capacity semiconductor devices. However, if the failure of defect of such high capacity semiconductor devices themselves is attended with the flow of excessive fault current through the devices, then the excessive fault current strikes an electric arc on the failed or defective semiconductor device to increase more and more the danger that circuitry adjacent to the arced device will be damaged. Therefore, it has been previously been common practice to dispose protective fuses externally of high power semiconductor devices to interrupt the excessive fault current. With a current capacity during normal operation exceeding 1,000 amperes, the protective fuse is required to increase in current capacity. However, if the protective fuse increases in current capacity, then the interrupting time thereof becomes accordingly long with the result that electrical energy on the order of several hundred kilowatt-seconds is generated within the arced semiconductor device until the protective fuse is fused off after the semiconductor device has been failed.
Upon the occurrence of a fault on a relatively central portion of the particular semiconductor substrate, the resulting fault current is conducted externally of the associated semiconductor device through electrodes connected to the substrate. Upon the occurrence of a fault on a relatively outer peripheral portion of the semiconductor substrate, the resulting fault current is concentrated on the fault portion until that portion has a very high current density. This results in the generation of a large quantity of electric energy on the fault portion sufficient to melt the semiconductor substrate or a metallic portion such as a diaphragm forming one part of an associated semiconductor device. Therefore, an electric arc at an elevated temperature is struck and sent forth externally of the semiconductor device. Under these circumstances, when an electrically charged portion is present externally of and adjacent to the arced device, the electric arc may shortcircuit the device with the charged portion, thus resulting in a serious accident such as an unexpected fire. Alternatively, high temperature gases evolved within the semiconductor device may be abruptly expanded, thus resulting in the danger that an enclosure for the semiconductor device might explode through that portion thereof having the lowest strength.
As above described, the manufacture of high capacity semiconductor devices might be attended with the danger that a fault occuring in such semiconductor devices will lead to a very significant accident.
Accordingly, it is an object of the present invention to provide a new and improved semiconductor device effective for preventing the abovementioned fault that may occur in high capacity semiconductor devices from resulting in the failure of an associated circuitry.
It is another object of the present invention to provide a new and improved semiconductor device free from the danger that an excessive fault current flowing through the device will lead to an explosion.